High-Discrimination Circular Polarization Detection Based on Dielectric-Metal-Hybrid Chiral Metamirror Integrated Quantum Well Infrared Photodetectors.

Circular polarization detection enables a wide range of applications. With the miniaturization of optoelectronic systems, integrated circular polarization detectors with native sensitivity to the spin state of light have become highly sought after. The key issues with this type of device are its low circular polarization extinction ratios (CPERs) and reduced responsivities. Metallic two-dimensional chiral metamaterials have been integrated with detection materials for filterless circular polarization detection. However, the CPERs of such devices are typically below five, and the light absorption in the detection materials is hardly enhanced and is even sometimes reduced. Here, we propose to sandwich multiple quantum wells between a dielectric two-dimensional chiral metamaterial and a metal grating to obtain both a high CPER and a photoresponse enhancement. The dielectric-metal-hybrid chiral metamirror integrated quantum well infrared photodetector (QWIP) exhibits a CPER as high as 100 in the long wave infrared range, exceeding all reported CPERs for integrated circular polarization detectors. The absorption efficiency of this device reaches 54%, which is 17 times higher than that of a standard 45° edge facet coupled device. The circular polarization discrimination is attributed to the interference between the principle-polarization radiation and the cross-polarization radiation of the chiral structure during multiple reflections and the structure-material double polarization selection. The enhanced absorption efficiency is due to the excitation of a surface plasmon polariton wave. The dielectric-metal-hybrid chiral mirror structure is compatible with QWIP focal plane arrays.

Combined role of polarization matching and critical coupling in enhanced absorption of 2D materials based on metamaterials.

Since 2D materials are typically much more efficient to absorb in-plane polarized light than out-of-plane polarized light, keeping the light polarization in-plane at the 2D material is revealed to be a crucial factor other than critical coupling in light absorption enhancement in a 2D material integrated with a light coupling structure. When the composite of a metal-insulator-metal structure and a 2D material changes from the magnetic resonator form to the metasurface Salisbury screen one, the field polarization at the 2D material changes from a mainly out-of-plane status to a mainly in-plane status. As a result, for graphene, the absorptance enhancement is increased by 1.6 to 4.2 times, the bandwidth enlarged by 3.6 to 6.4 times, and the metal loss suppressed by 7.4 to 24 times in the mid- to far-infrared range, leading to the absorptance of graphene approaching 90% in the mid-infrared regime and 100% in the THz regime. For monolayer black phosphorus, the absorptance enhancement at the wavelength of 3.5 µm is increased by 5.4 times, and the bandwidth enlarged by 1.8 times. For monolayer MoS2, the averaged absorptance in the visible-near infrared range is enhanced by 4.4 times from 15.5% to 68.1%.

Highly polarization-sensitive far infrared detector based on an optical antenna integrated aligned carbon nanotube film.

Polarization detection is another important way to characterize a light field in addition to intensity and spectrum. This is required for high-fidelity information acquisition and high precision target recognition in the infrared detection region. Single-wall carbon nanotube (SWCNT) films have been investigated for infrared detection with considerable sensitivity at room temperature based on the photothermoelectric effect. In this work, a bowtie antenna integrated aligned SWCNT film is proposed for highly polarization sensitive, far infrared detection. The SWCNT film is shaped into a belt and doped with diverse agents to form a p-n junction at the center. The SWCNTs are arranged perpendicular to the electronic transportation direction. The antenna is aligned at the junction and along the SWCNTs. Based on the following four factors: (1) deep-subwavelength light concentration at the junction, (2) alignment between the SWCNTs and the antenna, (3) anisotropic heat transfer in the aligned SWCNT film, and (4) light field reduction within the gap of the bowtie antenna for the polarization perpendicular to the antenna axis, the ratio between the responsivities for the polarizations parallel and perpendicular to the SWCNTs could be higher than 13 600. By changing the size of the antenna, the resonant frequency could be tuned. Over the range from 0.5 to 1.5 THz, the peak polarization extinction ratios at different resonant frequencies are all bigger than 700, and they are 16 to 320 times higher than that of the aligned SWCNT belt without the antenna. Moreover, the integration of the antenna and the aligned SWCNT belt also enhances the responsivity by 1 to 2 orders of magnitude. Compared to an aligned multi-wall carbon nanotube (MWCNT) film, an aligned SWCNT film integrated with an optical antenna is more favorable for highly polarization sensitive, far infrared detection. The result is based on the numerical simulations of the light and the thermal fields.